1. Field of the Invention
The present invention relates to a method for decoding received signals on the communication channels between at least one transmit antenna and plural receive antennas in the space-time coded direct sequence (DS)-CDMA communication system. More specifically, the present invention relates to a decoding method comprising steps of: adjusting the step-size which is an update unit for the tap weight vector for despreading received signals; updating the tap weight vector by use of the step-size; and despreading the received signals by use of the tap weight vector.
2. Description of the Related Art
Generally, adaptive blind multiuser detection is useful in the direct sequence (DS)-code division multiple access (CDMA) system, as it can suppress multiple-access interference (MAI) and inter-symbol interference (ISI) without any knowledge beyond that required for the conventional single-user detector. The adaptive blind multiuser detection method is implemented as the linear minimum mean square error (MMSE) detector using the blind least mean square (LMS) algorithm, and the adaptive interference canceller (AIC) using the modified blind LMS algorithm, etc. Such a blind LMS algorithm has a problem that the performance heavily depends on the step-size.
The step-size is a parameter μ multiplied with the estimation value of the instantaneous gradient of the mean square error (MSE) ∇ in the LMS algorithm (x(i+1)=x(i)+μ·∇). In the LMS algorithm, the variable x is adaptively updated, being proportional to the estimation value of the instantaneous gradient ∇ and the step size μ. As such, the step-size means an update unit for adaptively updating the variable x.
If the step size μ is too small, the speed of converging to an optimal value is too slow. If the step size μ is too large, the system may not converge and may diverge or be in an unstable state.